Field of the Invention
The present invention relates to a motor speed control method and system for improving the performance of a running resistance evaluation which prevents the driving force of a motor from transferring to vehicle wheels when evaluating a neutral gear running resistance of a Hybrid Electric Vehicle (HEV) to adjust the speed of a motor so that an input speed of a transmission is equal to an output speed of the transmission.
Description of Related Art
FIG. 3 is a diagram according to the prior art which illustrates an output torque difference of a vehicle wheel based on the speed of each individual vehicle when a running resistance is evaluated by a conventional method wherein a motor speed control is not provided. FIG. 4 is a diagram according to the prior art which illustrates a running resistance deviation based on the speed of each individual vehicle when a running resistance is evaluated by a conventional method wherein a motor speed control is not provided.
Referring to FIGS. 3 and 4, a neutral gear running resistance evaluation (e.g., coast-Down) for obtaining a road load coefficient to simulate a running load (e.g., roadbed state, wind state) of an actual road should be performed to receive a certificate for fuel efficiency of a vehicle. The results of the neutral gear running resistance evaluations with respect to mass-produced vehicles should be submitted to the certificate authority. Accordingly, the neutral gear running resistance evaluation (Coast-Down) is considered a key evaluation factor in the fuel efficiency certification.
More specifically, a vehicle is mounted on a dynamo during the neutral gear running resistance evaluation (Coast-Down), and the vehicle is forced to run at a substantially high speed or is driven on an actual road at a substantially high speed. Thereafter, the transmission of the vehicle is changed into the neutral gear, and the vehicle is adjusted to run the inertial mode. In this state, the running resistance coefficient is evaluated under the simulation of a running load (e.g., roadbed state, wind state, etc.). Particularly, the neutral gear running may be a running mode wherein the motor and a vehicle drive shaft are disconnected by the transmission to allow the wheels to rotate without power, and the vehicle is able to run in the inertial mode.
However, a reverse driving drag may occur during the running resistance evaluation of the hybrid electric vehicle, wherein the driving force of the motor transfers through the transmission to the wheels even though the transmission of the vehicle is in the neutral gear state. This phenomenon occurs since the driving force transfers in the sequence of an engine, an engine clutch, a motor, a transmission, a differential gear and wheels for a hybrid electric vehicle. Referring to FIG. 3, it may be possible to confirm a result of a neutral gear reverse driving drag evaluation of the transmission of each individual vehicle. In order words, since the reverse driving drags which occur at the same vehicle speed for each individual vehicle are different, it may be possible to confirm that the torques of the wheels occurring at the same vehicle speed are different in each individual vehicle. In addition, the torque deviation of the wheels has an effect on the deviation of a result of the running resistance during the running resistance evaluation (Coast-Down). In other words, since there is not any adjustment during the running resistance evaluation of the hybrid electric vehicle in the conventional art, the inertia of the motor may transfer through the transmission to the wheels, thus causing error in a result of the neutral running resistance evaluation.
Since the hybrid electric vehicle cannot run in the inertial mode due to the above-described phenomenon in the transmission, error may occur in a result of the running resistance evaluation, thus causing the deviation of the running deviation of each individual vehicle to increase. The transmission wherein the reverse driving drag has occurred may change vehicle loss, thus causing an error during the running resistance evaluation of each individual vehicle, which may result in the increased deviation of the running resistance of each individual vehicle. Referring to FIG. 4, as a result of the running resistance evaluation of each individual vehicle, it may be possible to confirm that the results of the running resistance of each individual vehicle are different from each other due to the neutral gear driving drag of the transmission, and a substantial amount of deviation may occur in the results of the running resistance of each individual vehicle.
Therefore, a motor speed control method is required for improving the performance of a running resistance evaluation of a hybrid electric vehicle which is able to remove any deviation of a running resistance between individual vehicles which has occurred due to the reverse driving drag of a transmission.